You don’t have to be a total narcissist to be a successful executive – but a solid dash of ego can help.

Self-aggrandizing individuals with a need for impact and power are slightly more likely to become leaders than the general population, according to a new study from researchers at the University of Illinois at Urbana-Champaign, the University of Nebraska at Lincoln and personality testing firm Hogan Assessment Systems. But while a dose of self-confidence is necessary to raise your hand for the top job and steer a big corporation, too much can cause a leader and company to falter.

The study, set to be published in the journal Personnel Psychology, analyzes 54 prior studies touching on narcissism. Some of those studies relied on surveys, which asked leaders whether they identify with statements like, “If I ruled the world, it would be a much better place” or “I think I’m a special person.” Others analyzed clues in shareholder letters: the number of self-references, for example (is it just a string of “I, I, I”?), or the size of the executives’ photos.

It’s helpful to think of narcissism as distributed along a spectrum. On one end, self-doubt isn’t a useful characteristic in a leader—they can look weak or have trouble making decisions, according to Peter Harms, one of the study’s authors and a management professor at the University of Nebraska-Lincoln. But individuals on the other end don’t take feedback well and can make reckless choices, he says.

Examples of too much self-confidence abound in the world of politics. Harms cites Jonathan Edwards, the former North Carolina senator and presidential candidate who spent lots of time grooming his hair and had an extra-marital relationship on the campaign trail, as displaying the vanity and self-centered nature emblematic of narcissists.

Another researcher went on the hunt for CEOs that display humility. Analyzing earnings call transcripts – comparing the number of times executives said “me” and “mine” versus “we” or “our,” for example – an Australian management expert compiled a list of the least narcissistic American CEOs. The line-up included Target’s Gregg Steinhafel, PepsiCo’s Indra Nooyi and Bank of America’s Brian Moynihan.

Rodney Warrenfeltz, who administers personality tests to high-level leaders as a managing partner at Hogan Assessments, uses what he calls “the bold scale” to measure where the corporate executives he works with fall along the continuum. The test incorporates statements that participants have to check off as true or false, such as, “I could get this country moving in the right direction.”

Warrenfeltz says a bold score of 70 to 90 on the 100-point scale signifies someone is truly confident. Anything above that can indicate arrogance or entitlement.

“When things go wrong, they blame other people,” he says of those who score at the very top of the scale. “When things go right they take the credit.”

In addition to narcissism, Harms, the University of Nebraska-Lincoln professor, studies other “dark traits” like Machiavellianism and psychopathy. (A 2010 study found that psychopaths are more likely to be found in the corner office than on the street.) At lower levels, these attributes can be useful in the corporate setting, he says—a little psychopathy often translates to being brave. A bit of Machiavellianism is really just political skill, being able to manipulate coworkers or sell people on an idea.

Harry Kraemer, a former CEO of the health-care company Baxter International Inc., says being able to influence people is a crucial part of effective leadership. He also thinks executives need “true self confidence,” a mentality where positive thoughts abound: “I know I’m good, I know I can add value, I’m going to make good decision, I’m going to get a lot of stuff done.”

But he also says humility is key. If an executive’s ego gets out of hand, employees won’t follow him or her.

Unless, of course, you’re someone like former Apple chief Steve Jobs– so intelligent and brilliant that the rules don’t really apply.

“If you’re that one-in-10-million person, even though you’ve got a mammoth ego, even though you don’t treat people very well, you’re so unusual that maybe people are willing to put up with it,” Kraemer says.

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